BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to a reception synchronization circuit, a reception
synchronisation method and a receiver, and particularly to a reception synchronization
circuit, a reception synchronization method, a receiver and a digital communication
system for receiving a synchronous word or a unique word (hereinafter referred to
as "UW") which is used to establish synchronization and transmitted in a predetermined
digital pattern for transmission of digital data in a satellite communication and
a mobile communication, for example, ICO system (Inmarsat-P Communication system),
Iridium system, Global Star system, CDMAOne system, GSM (Global System for Mobile
Communication) and W-CDMA system.
2. Description of the Related Art
[0002] Japanese Laid-open Patent Application No. Hei-1-256232 (prior art 1) discloses a
synchronous word (UW) detection system. The synchronous word detection system comprises
a line quality monitoring circuit for monitoring the quality of a line at any time
with a controller of a TDMA (Time Division Multiple Access) satellite communication
system and outputting line quality information at a predetermined time interval; a
permission error number setting circuit which receives the line quality information
and search/narrow mode information representing a reception synchronization process
in the TDMA satellite communication system to make the permission error number (threshold
value ε) of a synchronous word pattern of the satellite circuit variable in accordance
with the quality of the line at a predetermined time interval and output it; a threshold
value correlation detection circuit which receives the variable permission error from
the permissible error number setting circuit, compares reception input data with a
predetermined synchronous word pattern to establishment a correlation therebetween,
and then outputting a coincidence pulse on the basis of an indicated permission error
number ε; a storage circuit containing hardware information to exchange the permission
error number setting circuit and the threshold value correlation detection circuit
with each other on a real-time basis with the search/narrow information and the line
quality information as an input address; and a logic circuit for performing AND between
the coincidence pulse output from the threshold value correlation detection circuit
and an aperture signal occurring at a normal position of a reception reference burst
and outputting a synchronization detection pulse.
[0003] With the synchronous word system thus constructed, the UW detection can be efficiently
performed on a real-time basis, and particularly it can perform the detection of UW
efficiently when applied to an earth station having a compact-size antenna (1 to 2
m level) or an earth station in which deterioration of C/N due to attenuation of a
rainfall remarkably appears.
[0004] Japanese Laid-open Patent Application No. Hei-3-46429 (prior art 2) discloses a unique
word detection circuit apparatus including a code error rate measuring circuit for
measuring the code error rate of reception data input and outputting the code error
rate thus measured; a correlation detection threshold value calculation circuit for
calculating and outputting the correlation detection threshold value (ε) corresponding
to the code error rate; a microprocessor for outputting the correlation detection
threshold value (ε) with a bus signal; and a unique word detection circuit for judging
detection or miss detection of the correlation detection threshold value (ε) output
from the microprocessor and the reception unique word and then outputting a unique
word detection signal only when the unique word is detected.
[0005] With the unique word detection circuit apparatus thus constructed, loss of a unique
word due to temporary deterioration of a code error rate , loss of reception data
which is appendant to the loss of the unique word, and out-of-synchronization of a
line can be prevented, thereby enhancing synchronization precision and reliability.
[0006] Japanese Laid-open Patent Application No. Hei-3-70226 (prior art 3) discloses maximum
value detection selection means for selecting the reception signal having the maximum
envelope level from reception signals which are received by plural antennas; a limiter
circuit for dividing the reception signal having the maximum enveloped level thus
selected by the maximum envelope level to normalize the reception signal having the
maximum envelope level and set the envelope level to a predetermined value; means
for calculating a complex correlation coefficient between the normalized reception
signal and the complex signal corresponding to a specific frame synchronization pattern
(UW); and comparison means for comparing the complex correlation coefficient with
any threshold value level, wherein a frame synchronization detection circuit judges
the reception signal as a frame synchronization pattern (UW) when the complex correlation
coefficient is larger than the threshold value level.
[0007] Accordingly, in a reception apparatus using a diversity reception system, the effect
of multi-path fading can be removed, and the detection precision of the frame synchronization
pattern can be enhanced, so that there can be achieved a digital ground mobile radio
(wireless) communication system having high reception precision.
[0008] Further, Japanese Laid-open Patent Application No. Hei-5-167630 (prior art 4) discloses
a unique word detector including: a first delay detector for receiving as an input
signal a signal obtained by subjecting quasi-synchronization and demodulation to a
reception signal in which a unique word is inserted, and detecting the delay of the
input signal; a unique word generator for generating a complex conjugate value of
the unique word; a second delay detector for detecting the delay of the output of
the unique word generator; a mutual correlator for taking a mutual correlation between
the first and second delay detectors; and a level detector for comparing the output
of the mutual correlator with a predetermined threshold value to detect the maximum
value thereof.
[0009] With the unique word detector thus constructed, the input signal is subjected to
the delay detection by the first delay detector to remove a frequency offset therefrom,
and then input to the mutual correlator while a frequency offset is removed therefrom.
Therefore, even when an input signal has large frequency instability, it is unnecessary
to arrange many mutual correlators in parallel for use unlike the prior art, and thus
the circuit scale can be greatly reduced. In addition, only one input signal is supplied
to the level detector, so that the error detection probability can be reduced.
[0010] However, in the prior arts 1 to 4, the detection means of UW itself is shown, and
it is applicable to a case where a received status is surely stable. However, when
the received status is unstable, an error detection state occurs in UW itself, and
thus UW detection which takes no consideration into the received status is little
accurately performed. Further, a predetermined time is needed to detect the correlation
of UW, and when the correlation of UW is taken although the received status is bad,
time is merely wasted.
[0011] In the prior art 4, the level detection is performed by the quasi-synchronized and
modulated signal of the reception signal and the unique word generator for generating
the complex conjugate of UW. In this prior art, the level detection is accurate, however,
the relationship between the level detection and the detection of UW is not clarified.
[0012] That is, when a reception frequency at which a reception signal exists is not known
at an initial stage, the reception electric field intensity of the reception signal,
that is, the reception power is first detected in order to establish an early synchronization
between the reception frequency and the clock timing. At this time, in the case where
the detection level of the reception power is judged on the basis of only one threshold
value, the reception power is frequently judged as a noise if the threshold value
is low, and thus erroneous detection frequently occurs. On the other hand, if the
threshold value is high, the detection of the reception signal is missed. When the
reception electric field intensity, that is, the detection level of the reception
power is low, the probability that the detection error is increased is high, and thus
it has been still required to perform accurate UW detection with a simple construction.
SUMMARY OF THE INVENTION
[0013] Therefore, an object of the present invention is to reduce the noise error detection
and the signal miss detection by preparing one type or two or more types of threshold
values for a movement average detected and calculated on the basis of received power
and using an improved judgment algorithm.
[0014] Further, another object of the present invention is to enable adaptive controls in
various communication states by storing various past detection situations to feed
back them to the setting of a threshold value.
[0015] Still further, further other object of the present invention is to keep an early
realization of synchronization establishment by achieving a retrial of a maximum UW
measurement.
[0016] In order to attain the above objects, according to a first aspect of the present
invention, a reception synchronization circuit for receiving a unique word transmitted
in a predetermined digital pattern is characterized by comprising: a detection circuit
for outputting a reception movement average of a received signal; a memory for storing
at least one threshold value for the movement average; comparison means for comparing
the reception movement average and the threshold value of the movement average; and
an UW correlation judgment circuit for detecting the unique word (hereinafter referred
to as "UW") when the reception movement average is higher than the threshold value
of the movement average, and taking a correlation between the detected unique word
and a predetermined digital pattern.
[0017] Further, according to a second aspect of the present invention, a reception synchronization
circuit for receiving a unique word transmitted in a predetermined digital pattern
is characterized by comprising: a detection circuit for detecting the received power
of a received signal and outputting a movement average; a UW correlation judgment
circuit for detecting the unique word (hereinafter referred to as "UW") and taking
a correlation between the unique word thus detected and a predetermined digital pattern;
and a memory for storing two or more threshold values for the movement average, wherein
after the two or more threshold values and the movement average are compared with
each other, the correlation is taken by the UW correlation judgment circuit when the
movement average is larger than the minimum values of the two or more threshold values.
[0018] In the above reception synchronization circuit, when the movement average is larger
than the maximum threshold value of the two or more threshold values, the correlation
is taken by the UW correlation judgment circuit. Further, when the movement average
is smaller than the minimum threshold value of the two or more threshold values, the
minimum threshold value is increased.
[0019] According to a third aspect of the present invention, a receiver according to the
present performs data detection based on the TDMA system by using the above reception
synchronisation circuit.
[0020] According to a fourth aspect of the present invention, a reception synchronisation
method for receiving a unique word (hereinafter referred to as "UW") transmitted in
a predetermined digital pattern is characterized by comprising the steps of: detecting
the received power of a received signal; calculating the mean square of the received
power and outputting a reception movement average; reading out from a memory the minimum
threshold value and the maximum threshold value which are stored in the memory in
advance; comparing the reception movement average with the minimum threshold value;
detecting the UW when the reception movement average is larger than the minimum threshold
value; and taking a correlation between the UW and the predetermined digital pattern.
[0021] In the above reception synchronization method, when the reception movement average
is judged to be smaller than the minimum threshold value as a result of the comparison
between the reception movement average and the minimum threshold value, the minimum
threshold value is reduced to search a next reception channel. Further, in the above
reception synchronization method, when the reception movement average is judged to
be larger than the minimum threshold value and smaller than the maximum threshold
value as a result of the comparison of the reception movement average, the minimum
threshold value and the maximum threshold value, the maximum threshold value is reduced
to perform a correlation calculation between the received signal and the UW.
[0022] According to a fifth aspect of the present invention, a digital communication system
according to the present invention performs synchronization by using the above reception
synchronisation method.
[0023] Specifically, the signal detection and synchronization are established by the power
detection and the UW (Unique Word) correlation. At this time, the judgment of the
detection is performed on the basis of the threshold value, and two kinds of threshold
values are prepared for the power detection to enhance the early search and the detection
probability. Further, the past results are beforehand stored to suitably renew the
threshold value.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024]
Fig. 1 is a diagram showing a signal construction of a data format according to the
present invention;
Fig. 2 is a block diagram showing the construction of an embodiment of the present
invention;
Fig. 3 is a block diagram showing an input frequency setting circuit according to
an embodiment of the present invention;
Fig. 4 is a block diagram showing a reception power detection circuit according to
the embodiment of the present invention;
Fig. 5 is a graph showing the relationship between a movement average and an error
rate used in the embodiment of the present invention;
Fig. 6 is a block diagram showing a UW correlation judgment circuit according to the
embodiment of the present invention;
Fig. 7 is a block diagram showing a decoder according to the embodiment of the present
invention;
Fig. 8 is a flowchart showing the embodiment of the present invention;
Fig. 9 is a waveform diagram showing the embodiment of the present invention;
Fig. 10 is a block diagram showing the construction of the embodiment of the present
invention; and
Fig. 11 is a flowchart showing the embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Preferred embodiments according to the prevention invention will be described hereunder
with reference to the accompanying drawings.
[First Embodiment]
[0026] A first embodiment according to the present invention will be described hereunder
with reference to the accompany drawings.
[0027] Fig. 1 shows the data format of a synchronous burst containing a unique word (hereinafter
referred to as "UW") used for TDMA (Time Division Multiple Access) system. The synchronous
burst can be received at a synchronous frame interval by demodulating a received signal
of a specific control channel. The synchronous burst is formatted by control data,
UW formed of a predetermined digital pattern and control data. However, the format
of the synchronous burst containing UW is not limited to the above format, and other
formats may be adopted.
[0028] Fig. 2 is a block diagram showing the construction of a reception synchronization
circuit according to the first embodiment.
[0029] In a reception synchronization circuit shown in Fig. 2, reference numeral 1 represents
a power detection circuit of a received signal, reference numeral 2 represents a UW
correlation judgment circuit of UW of the received signal, reference numeral 3 represents
a control CPU for controlling the overall reception synchronization circuit, reference
numeral 4 represents a rewritable memory for storing plural threshold values for a
movement average which is detected and calculated on the basis of the received power,
and a correlation detection threshold value (ε) used in the UW correlation judgment
circuit, reference numeral 5 represents an input frequency setting circuit for demodulating
a received input signal and outputting orthogonal signals I and Q, which contains
a high-frequency unit, a mixer circuit, an intermediate frequency unit, a demodulation
circuit, etc. and can set the received channel, and reference numeral 6 represents
a data processor for establishing synchronization on the basis of the received UW,
processing the received data and outputting a demodulated signal.
[0030] According to the reception synchronization circuit thus constructed, the input frequency
setting circuit sets the frequency of a local oscillation unit for the received input
signal from a reception antenna (not shown) according to a received channel indicated
by CPU 3, and the received signal is passed through a high-frequency amplifier, a
mixer circuit, an intermediate frequency amplifying circuit and a digital signal demodulation
circuit and then orthogonally demodulated and output as I, Q signals as in the case
of QPSK or the like.
[0031] Fig. 3 shows the construction of the input frequency setting circuit 5.
[0032] In Fig. 3, the high frequency signal input from the reception antenna is input through
the high frequency amplifying circuit and a high frequency filter to a mixer 51, and
a synthesizer generates a local oscillation signal corresponding to the received frequency
on the basis of a frequency setting signal of the CPU 3 and inputs the local oscillation
signal to the mixer 51. The mixer 51 outputs an intermediate frequency signal. The
intermediate frequency signal has a frequency of about 10MHz and demodulated by a
quasi synchronization detection circuit. In the quasi synchronization detection circuit,
the intermediate frequency signal is multiplied with an oscillation signal of a reference
oscillator 56 in a first multiplier 53, converted to a digital signal in an A/D converter
57 and then output as an I signal. The intermediate frequency signal is multiplied
with an inverted oscillation signal in a second multiplier, the inverts oscillation
signal being output through a π/2 phase-shifter 55 for inverting the phase of the
oscillation signal of the reference oscillator 56, and then converted to a digital
signal in an A/D converter 58 to be outputted as a Q signal.
[0033] In the power detection circuit 1, the electric field intensity of the input received
signal, that is, the received power of the received signal can be achieved by detecting
the envelope level of the carrier of the intermediate frequency unit of the input
frequency setting circuit 5, and in the following description, a detection circuit
for the movement average shown in Fig. 4 will be described.
[0034] In Fig. 4A, the square values of I, Q signals are achieved through the multipliers
11, 12 respectively on the basis of I, Q signals which are orthogonally demodulated
in the input frequency setting circuit 5, then these square values are added to each
other by an adder 13 to achieve I
2 + Q
2, and then a movement average is output by a movement average circuit 14. In a comparator
15, the movement average thus obtained is compared with threshold values 1, 2 output
from the memory 4 through lines 103, 104, and the comparison result is output as a
power detection output to the CPU 3.
[0035] Here, Fig. 4B shows the general relationship between the synchronisation pattern
and the movement average.
[0036] The synchronization pattern is a synchronous burst containing UW within a periodic
synchronous frame. The movement average is different in pulse form from the synchronous
burst, however, it is gradually increases from the detection time of the synchronous
burst and gradually reduced from the extinction time of the synchronous burst. A window
may be applied during the period of the synchronous burst, however, the movement average
is detected as a triangular wave.
[0037] The position of the peak of the triangular wave is dependent on the digital pattern
of the synchronous burst on the assumption that it has no noise component, and it
is beforehand set to a position which is determined by a synchronous burst generated
in the communication system. That is, it is predetermined that UW is started at a
preceding position or subsequent position by several bits from the peak position of
the triangular wave of the movement average, so that the start point of UW can be
settled by using a substantially predetermined number of bits. Further, the movement
average is compared with the threshold values 1, 2 in the comparator 15. The power
of the received signal can be detected by comparing the movement average with one
threshold value, and if UW is afterwards detected and correlated, it is effective
for the UW correlation and detection. However, in order to perform UW detection more
accurately, it is better to compare the movement average with two or more threshold
values, whereby the degree of the movement average represented by the received power
can be accurately detected.
[0038] Fig. 5 shows a graph showing the relationship between the movement average and the
error rate. A miss detection line (Miss Detection) represents a characteristic when
no UW is detected in spite of presence of a received signal. In this miss detection
line, the error rate of UW is a high value when the movement average is large, however,
the error rate of the miss detection is low value when the movement average is small.
In this case, when C/N of the received signal is low, that is, when the noise component
is large (represented by a dotted line in Fig. 5), the error rate is higher than the
error rate P1m of the miss detection line when the movement average is equal to the
threshold value 1. This is because the detection of the received signal is more frequently
carried out due to a large noise.
[0039] Further, an error detection line (False Detection) represents a characteristic when
UW is detected as an error detection although the noise component is large. When the
movement average is large, the error rate of the error detection of UW is reduced.
On the other hand, when the movement average is small, the error rate of the error
detection of UW is increased.
[0040] Fig. 6 shows a circuit diagram of the UW correlation judgment circuit 2. In the UW
correlation judgment circuit 2, the orthogonal signals I, Q are converted to a parallel/serial
signal Y(t) in a P/S circuit 21, and then Y(t) is adjusted in its timing by a delay
circuit 22 and input to a mutual correlator 23 to be correlated with a reference S(t)
which is UW of a predetermined digital pattern of a line 201. The output of the mutual
correlator 23 is compared with the correlation detection threshold value (ε) of a
line 202, and it is judged on the basis of the correlation probability whether UW
is detected or not. Thereafter, the judgment result is output as a UW detection signal
from a line 203.
[0041] The decoder 6 contains so-called DEM in the data processor, and the construction
thereof is shown in Fig. 7. The orthogonal signal I, Q is input to a delay unit 61
in which the mutual timings of the orthogonal signals I, Q are matched with each other
by a delay time adjustment signal τ from the CPU 3. In Fig. 7, the units from the
delay unit 61 to an identifier 66 are illustrated as one system. However, these units
are actually provided as two systems for the orthogonal signals I, Q, respectively,
and only one system is illustrated in Fig. 7 for convenience's sake. The I signal
or Q signal passed through the delay unit 61 is complex-multiplied with the output
of a numerical control oscillator NCO 63 by a complex multiplier 62, and the complex-multiplied
I signal or Q signal is input to a carrier reproducing circuit 64 to generate a numeral
control signal and input to NCO 63. Further, the I signal or Q signal is subjected
to timing correction in a clock reproducing circuit BTR 65 serving as a bit timing
recovery circuit, and then original transmitted data are output on the basis of the
input I signal or Q signal by the identifier 66. A described above, the UW detection
signal detected by the UW correlation judgment circuit 2 is input to the CPU 3, the
delay time adjustment signal τ is accurately generated on the basis of the UW detection
signal, and data detection can be performed with high reliability in the demodulator
6.
[0042] Next, the operation of the reception synchronization circuit described above will
be described in detail with reference to the flowchart of Fig. 8 by using an example
of the detection level of the movement average for a synchronous burst (a) of Fig.
9.
[0043] In Fig. 8, the first power measurement of the received signal is performed in step
11 to calculate and detect the movement average. Subsequently, in step 12, the movement
average which is the power level of the received signal is compared with a threshold
value 1 and a threshold value 2. However, the threshold value 1 is set to be larger
than the threshold value 2. As a result of the comparison, when it is judged that
the received power level is larger than the threshold value ((b) of Fig. 9), the processing
goes to step 18 for UW detection. When it is judged that the received power level
is between the threshold values 1 and 2 ((c), (d) of Fig. 9), the power measurement
is performed again during the period of the second synchronous burst signal, and the
power level is compared with the threshold value 2 in step 14. If the power level
is larger than the threshold value 1 in step 14 ((c) of Fig. 9), the threshold value
1 is renewed to be increased in step 15, and then the processing goes to Step 18 for
UW detection. If the power level is smaller than the threshold value 1 in step 14
((d) of Fig. 9), the processing goes to step 22 to renew the threshold value 2 so
that the threshold value 2 is increased, and then the processing goes to step 17.
[0044] Further, if the received power level is smaller than the threshold value 2 in step
12 ((e) of Fig. 9), it is judged that no signal exists in the received channel concerned,
and the threshold value 2 is renewed to be reduced in step 16. Thereafter, the processing
is shifted to a next received channel frequency in step 17, and the processing returns
to step 11 again to set the next received channel and start the power measurement.
[0045] For the signal for which the power level of the movement average above the threshold
value 1 is detected, the correlation between UW read out from the memory 4 and UW
of the received signal are temporarily calculated in step 18. In step 19, the correlation
value is compared with the UW threshold value (ε). If the correlation value is larger
than the UW threshold value (ε), the threshold value 1 and the threshold value 2 are
left as they are in step 20. Thereafter, the signal data detection is performed in
the data processor 6, and the processing is normally finished. This means that the
correct signal is received, and the signal processing for the received data, sounds,
etc. is carried out.
[0046] Next, if the UW correlation value thus received is smaller than the UW threshold
value (ε) in step 19, the route of the steps along which the processing is carried
out is estimated in step 21, the threshold value 1 is increased while the threshold
value 2 is left as it is, and then the processing is shifted to hopping to the next
received channel in step 17.
[0047] In the above flowchart, the upper and lower limits are preset for the threshold value
of the received power level, and the setting of the threshold value is adjusted so
that the threshold value does not exceed the range determined by the upper and lower
limits when the adaptive control is performed.
[0048] Here, the threshold value 1 of the movement average is reduced when the frequency
of the miss detection is high, and it is increased when there is no miss detection
and the UW correlation trends to be further higher than the UW threshold value (ε)
or the frequency of the error detection is large.
[0049] Further, the threshold value 2 is increased when the frequency of the error detection
is excessively high, and it is reduced when there is any miss detection or there is
no error detection and the UW correlation trends to be further higher than the UW
threshold value (ε). The UW threshold value (ε) is not renewed after it is set at
an initial stage.
[0050] In the above flowchart, the comparison/judgment based on the past threshold values
in the first power measurement and the second power measurement are performed to store
the past results, whereby the threshold value can be renewed adaptively.
[0051] As described above, the threshold values 1, 2 are renewed in accordance with the
movement average received and detected, so that the accuracy and the reliability of
the UW detection can be enhanced.
[Second Embodiment]
[0052] Next, a reception synchronization circuit according to a second embodiment will be
described.
[0053] Figs. 10 and 11 are a block diagram and a flowchart of a receiver according to this
embodiment. In Fig. 10, the difference from Fig. 2 resides in that a renewal frequency
detection circuit 7 connected to the power detection circuit 1 and the UW correlation
judgment circuit 2. Further, in the flowchart of Fig. 11, the difference from Fig.
8 resides in that each flow route contains route count steps 23 to 27, and a renewal
method and a renewal step are judged when the threshold values 1, 2 are renewed.
[0054] In Fig. 10, the renewal frequency detection circuit 7 receives the difference between
the threshold value 1,2 and the received movement average from the power detection
circuit 1 and the difference between the UW received from the UW correlation judgment
circuit 2 and the correlation threshold value stored in the memory 4 to detect the
renewal step of each threshold value 1,2 and input the data thereof to the CPU 3.
The renewal step is set in the CPU 3, the threshold value of the memory 4 is increased
or reduced in the renewal step and stored in the memory 4, and finally there are provided
for comparison with plural threshold values in the power detection circuit 1.
[0055] In Fig. 11, when each threshold value for the movement average is renewed, the route
count 23 represents a route of a first measurement result, and it is used in renewal
steps 20, 21 of the threshold value 1. The route count 24 represents a route of a
second judgment result, and it is used in renewal steps 15, 20, 21. A route count
25 represents a route of a second judgment result, and it is used in a renewal step
22 of the threshold value 2. Further, it is effectively used in the renewal step for
route counts 26, 27.
[0056] For example, in the case where the threshold value 21 is renewed in step 21, when
the processing passes from the step 12 through the steps 23, 18, 19, it corresponds
to a case where the movement average is larger than the threshold value 1, but UW
cannot be normally detected in the first step of (b) of Fig. 9. Therefore, the noise
component is estimated as being large, and the renewal is made to increase threshold
value 1. However, when the processing passes from the step 12 through the steps 13,
14, 24, 18, 19, it corresponds to a case where the movement average is larger than
the threshold value 1, but UW cannot be normally detected in the second step of (c)
of Fig. 9, and thus the detection is estimated to be made due to the noise component
in the second step, so that the threshold values 1 and 2 are increased, and the channel
is judged to have no received signal to wait for reception of a next channel.
[0057] Further, in the case of the renewal of the threshold value in step 20, when the processing
passes from the step 12 through the steps 13, 13, 24, 15 and 19, it corresponds to
a case where the movement average is larger than the threshold value 1 in the second
step of (c) of Fig. 9 and UW can be normally detected, and thus the renewal is made
to increase the threshold value 1 and leave the threshold value 2 as it is in order
to make the first detection normal.
[0058] Still further, when the received signal level is high, the processing passes through
the route count 23 and UW is larger than the UW threshold value, it is effective to
increase the current threshold value 1 by two steps or three steps in the renewal
step 20 of the threshold value 1.
[0059] As described above, the route along which the processing passes in the route of the
flowchart shown in Fig. 11 varies the renewal state of the threshold value, and thus
it is effective as an optimizing method.
[0060] The gap between the threshold values 1 and 2 may be controlled so as to be larger
so that the probability that there is a received signal and it is larger than the
threshold value 1 and the probability that there is a received signal and it is between
the threshold values 1 and 2 are constant.
[0061] Particularly, the system which is effective to each of the above embodiments uses
as a received signal having UW BCCH (Broadcast control channel) signal used in a GSM
terminal device or the like. However, it may be applied to various portable terminals
using TDM system receiving like signals, such as a portable communication terminal,
PHS (Personal Handyphone System).
[0062] In each embodiment, the estimation of the synchronization frequency and the clock
timing is made on the basis of the received signal having UW. In this case, the present
invention is effective even when it contains a circuit for making such an estimation
in combination with other synchronizing signals such as a carrier reproducing pulse,
a clock reproducing pulse or the like.
[0063] According to the present invention, the two threshold values for received power detection
are provided, and the probability that the error detection of detecting a noise as
a signal is carried out can be reduced by using a higher threshold value. Further,
the probability that the miss detection of the received signal is carried out can
be reduced by using the lower threshold value.
[0064] Further, the probability of the error detection and the miss detection can be reduced
by performing the adaptive control on the threshold value on the basis of the past
detection results. In addition, the total judgment frequency can be reduced, and the
early establishment of the synchronization can be performed (two periods are required
at maximum per channel, however, the frequency of the two-period measurement can be
reduced if the threshold value is adaptively set).
[0065] Next, the correlation between the received power level and the error detection of
UW will be described.
[0066] For example, when the probability that the measurement received power is larger than
the threshold value 1 is represented by (1 - p1m) (p1m: probability of miss detection),
the probability of the error detection at that time is represented by p1f, the probability
that the miss detection is carried out with the threshold value 2 is represented by
p2m and the probability of the error detection is represented by p2f, the probability
that the correction detection is carried out in the first step is represented by (

), and the probability that the correction detection is carried out in the second
step is represented by (

). Therefore, the probability of the correction detection in the total of the first
and second steps is represented as follows:

[0067] The threshold value for the received power which is the movement average optimum
to the UW detection is set on the basis of this correlative relationship, whereby
the optimum setting method can be established.
1. A reception synchronization circuit for receiving a unique word transmitted in a predetermined
digital pattern comprising:
a detection circuit for outputting a reception movement average of a received signal;
a memory for storing at least one threshold value for the movement average;
comparison means for comparing the reception movement average and the threshold value
of the movement average; and
an UW correlation judgment circuit for detecting the unique word (hereinafter referred
to as "UW") when the reception movement average is higher than the threshold value
of the movement average, and taking a correlation between the detected unique word
and a predetermined digital pattern.
2. The reception synchronisation circuit as claimed in claim 1,
wherein the threshold value stored in said memory is made variable.
3. A reception synchronization circuit for receiving a unique word transmitted in a predetermined
digital pattern comprising:
a detection circuit for detecting the received power of a received signal and outputting
a movement average;
a UW correlation judgment circuit for detecting the unique word (hereinafter referred
to as "UW") and taking a correlation between the unique word thus detected and a predetermined
digital pattern; and
a memory for storing two or more threshold values for the movement average, wherein
after the two or more threshold values and the movement average are compared with
each other, the correlation is taken by said UW correlation judgment circuit when
the movement average is larger than the minimum values of the two or more threshold
values.
4. The reception synchronization circuit as claimed in claim 3,
wherein when the movement average is larger than the maximum threshold value of the
two or more threshold values, the correlation is taken by said UW correlation judgment
circuit.
5. The reception synchronization circuit as claimed in claim 3,
wherein when the movement average is smaller than the minimum threshold value of the
two or more threshold values, the minimum threshold value is increased.
6. The reception synchronization circuit as claimed in claim 3,
wherein at least two threshold values stored in said memory are made variable.
7. The reception synchronization circuit as claimed in claim 4,
wherein at least two threshold values stored in said memory are made variable.
8. The reception synchronization circuit as claimed in claim 5,
wherein at least two threshold values stored in said memory are made variable.
9. A receiver which detects data based on TDMA system by using a reception synchronization
circuit for receiving a unique word transmitted in a predetermined digital pattern,
said reception synchronization circuit comprising:
a detection circuit for detecting the received power of a received signal and outputting
a movement average;
a UW correlation judgment circuit for detecting the unique word (hereinafter referred
to as "UW") and taking a correlation between the unique word thus detected and a predetermined
digital pattern; and
a memory for storing two or more threshold values for the movement average, wherein
after the two or more threshold values and the movement average are compared with
each other, the correlation is taken by said UW correlation judgment circuit when
the movement average is larger than the minimum values of the two or more threshold
values.
10. The receiver as claimed in claim 9,
wherein when the movement average is larger than the maximum threshold value of the
two or more threshold values, the correlation is taken by said UW correlation judgment
circuit.
11. The receiver as claimed in claim 9,
wherein when the movement average is smaller than the minimum threshold value of the
two or more threshold values, the minimum threshold value is increased.
12. The receiver as claimed in claim 9,
wherein at least two threshold values stored in said memory are made variable.
13. A receiver which detects data based on CDMA system by using a reception synchronization
circuit for receiving a unique word transmitted in a predetermined digital pattern,
said reception synchronization circuit comprising:
a detection circuit for detecting the received power of a received signal and outputting
a movement average;
a UW correlation judgment circuit for detecting the unique word (hereinafter referred
to as "UW") and taking a correlation between the unique word thus detected and a predetermined
digital pattern; and
a memory for storing two or more threshold values for the movement average, wherein
after the two or more threshold values and the movement average are compared with
each other, the correlation is taken by said UW correlation judgment circuit when
the movement average is larger than the minimum values of the two or more threshold
values.
14. The receiver as claimed in claim 13,
wherein when the movement average is larger than the maximum threshold value of the
two or more threshold values, the correlation is taken by said UW correlation judgment
circuit.
15. The receiver as claimed in claim 13,
wherein when the movement average is smaller than the minimum threshold value of the
two or more threshold values, the minimum threshold value is increased.
16. The receiver as claimed in claim 13,
wherein at least two threshold values stored in said memory are made variable.
17. A reception synchronization method for receiving a unique word (hereinafter referred
to as "UW") transmitted in a predetermined digital pattern comprising the steps of:
detecting the received power of a received signal;
calculating the mean square of the received power and outputting a reception movement
average;
reading out from a memory the minimum threshold value and the maximum threshold value
which are stored in the memory in advance;
comparing the reception movement average with the minimum threshold value;
detecting the UW when the reception movement average is larger than the minimum threshold
value; and
taking a correlation between the UW and the predetermined digital pattern.
18. The reception synchronization method as claimed in claim 17,
wherein when the reception movement average is judged to be smaller than the minimum
threshold value as a result of the comparison between the reception movement average
and the minimum threshold value, the minimum threshold value is reduced to search
a next received channel.
19. The reception synchronization method as claimed in claim 17,
wherein when the reception movement average is judged to be larger than the minimum
threshold value and smaller than the maximum threshold value as a result of the comparison
of the reception movement average, the minimum threshold value and the maximum threshold
value, the maximum threshold value is reduced to perform a correlation calculation
between the received signal and the UW.
20. A digital communication system which establishes synchronization by using a reception
synchronization method for receiving a unique word (hereinafter referred to as "UW")
transmitted in a predetermined digital pattern, the reception synchronization method
comprising the steps of:
detecting the received power of a received signal;
calculating the mean square of the received power and outputting a reception movement
average;
reading out from a memory the minimum threshold value and the maximum threshold value
which are stored in the memory in advance;
comparing the reception movement average with the minimum threshold value;
detecting the UW when the reception movement average is larger than the minimum threshold
value; and
taking a correlation between the UW and the predetermined digital pattern.
21. The digital communication system as claimed in claim 20,
wherein when the reception movement average is judged to be smaller than the minimum
threshold value as a result of the comparison between the reception movement average
and the minimum threshold value, the minimum threshold value is reduced to search
a next received channel.
22. The digital communication system as claimed in claim 20,
wherein when the reception movement average is judged to be larger than the minimum
threshold value and smaller than the maximum threshold value as a result of the comparison
of the reception movement average, the minimum threshold value and the maximum threshold
value, the maximum threshold value is reduced to perform a correlation calculation
between the received signal and the UW.